ScanSAR image of eddies in the Weddell Sea.
ScanSAR image of eddies in the Weddell Sea. ©

The Weddell Gyre is a large system of rotating currents located in the Weddell Sea, Antarctica. The gyre facilitates the exchange of waters between the vast Antarctic Circumpolar Current (ACC) that encircles Antarctica and the waters of the continental shelf.

In the Weddell Sea, waters become cooler and more saline as sea ice forms. This leads to an increase in density, causing overturning of the water column. This results in nutrients, carbon and oxygen from near-surface waters being mixed downward into the Antarctic Bottom Water (AABW), a deep water mass that forms in the Weddell Sea. The AABW flows northward out of the Weddell Sea and ventilates deep ocean waters.

Overturning circulation is important for deep water ventilation across the World Ocean and is made possible by sea ice processes in both the Arctic and Antarctic Oceans. Surface currents transport waters towards the poles, where they become dense and sink, before flowing toward the equator as deep ocean currents. This contributes to the Meridional Overturning Circulation (MOC), which helps to regulate global temperatures and plays a crucial role in world climate.

The MOC ensures that the deep oceans remain ventilated and conducive to life. It is also important for the sequestration — removal from the atmosphere and long-term storage — of anthropogenic carbon. The overturning that occurs in the Weddell Sea forms the southern closure of the MOC, so the role of the Weddell Gyre in the exchange of Southern Ocean water masses is important on a global scale.

The ANDREX programme aims to investigate the exchange of water masses between the ACC and the Weddell Sea, as well as rates of formation and ventilation of AABW within the gyre. It will study carbon and nutrient cycles and investigate the role of the gyre in anthropogenic carbon sequestration. The work will also investigate inputs of fresh water to the gyre, including the roles of sea ice, precipitation and glacial melt.

Antartic Deep Water Rates of Export (ANDREX)